Conventionally, to dynamically correct aberration in an image-formation optical system, there has been known an aberration correction device using a liquid crystal panel. Such an aberration correction device is fabricated in a manner such that transparent electrodes of its liquid crystal panel are formed by virtue of divided areas having aberration correction patterns, and aberration correction is performed by providing a phase difference corresponding to a divided area to a light beam passing through the liquid crystal panel, by virtue of an electro-optic effect of the liquid crystal panel.
Such an aberration correction device is used in an image-formation optical system of an optical pickup which converges a light beam emitted from a light source on to a recording surface of an optical information recording medium, while a reflection light from the recording surface is formed into an image on a detection surface of a detector. In such an image-formation optical system, a coma aberration occurred due to a tilt or the like of an optical information recording medium, a spherical aberration occurred due to a thickness error of an optical recording medium, an astigmatism occurred due to distortion of optical parts of the optical pickup will each bring about a significant unfavorable influence on a recording/reproducing performance. As a result, the foregoing three kinds of aberrations have become correction objects for an aberration correction device to deal with. In using the above-described aberration correction device having a liquid crystal panel, when an aberration correction is performed, it is required to find a wave surface aberration distribution of each aberration in a pupil surface of an objective lens, so as to form an electrode pattern consisting of divided areas in transparent electrode of the liquid crystal panel inserted in an image-formation optical system, in response to the wave surface aberration distribution.
For example, the following patent document 1 has disclosed an optical pickup having a laser light source, an objective lens, and an aberration correction means consisting of a liquid crystal panel provided on an optical axis of a laser beam. In such an optical pickup, one transparent electrode of the liquid crystal panel consisting of a pair of transparent electrodes is used as a first electrode divided into a pattern corresponding to a wave surface aberration distribution of a coma aberration in a pupil surface of an objective lens, while the other transparent electrode is used as a second electrode divided into a pattern having a converging function for correcting a spherical aberration.
Moreover, the patent document 1 has disclosed that one electrode of a pair of transparent electrodes in the liquid crystal panel forming an aberration correction means is divided into a pattern corresponding to a wave surface aberration distribution of a coma aberration in a pupil surface of the objective lens, as well as a pattern for correcting a spherical aberration.
The following patent document 2 has disclosed another aberration correction device using a similar liquid crystal panel, in which a light beam passing area of the liquid panel is divided into a plurality of portions corresponding to an astigmatism distribution, while voltages corresponding to the directions of the astigmatisms to be corrected are applied to the electrodes provided in the divided areas, and a phase difference for correcting an astigmatism is provided to a light beam passing through each divided area in response to a voltage change.
Patent document 1: Japanese Unexamined Patent Application Publication No. (Hei) 10-289465.
Patent document 2: Japanese Unexamined Patent Application Publication No. 2000-40249.